» Even as Dallas finishes work on a new light rail line, plans for a new highway along a parallel corridor advance.

This summer, Dallas’ Orange Line will be extended five stations northwest of downtown. The light rail service will expand what is already the United States’ longest such network and improve connections between central Dallas, the suburb of Irving, and — in 2014 — Dallas-Fort Worth International Airport. Yet billions of dollars in new construction have barely increased transit use; just 4.2% of the city’s commuters use public transportation to get to work, according to the U.S. Census Bureau. If there is one city that proves that simply building transit does not attract people to transit, this is it.

Investments in Dallas’ road infrastructure might provide some explanation for the situation. An astonishing seven grade-separated highways extend radially out from the city center in all directions.* This is a

» A 1.6-mile streetcar line would bring dubious benefits to this Texas city.

Not all transit expansion projects are created equal — let that be clear. Sure, expanding public transportation options in general usually contributes to the expanded mobility of urban residents. But governments, as we know all too well, have limited funds. So identifying the best possible investments for the money must be an essential part of political decision-making.

There are many competing reasons to invest in new transportation capacity, the most compelling of which is often to expand mobility — that is, to increase the number of places an individual can get to within a certain period of time. The need to decrease travel times between major destinations is an essential question for transit, since its major competition, the private automobile, usually provides quicker, more convenient trips.

In cities with high levels of highway capacity per capita, the only transit mode that can compete relatively well in terms of mobility is commuter rail, as its limited stopping pattern and sometimes very high speeds allow it to move faster than even free-flow traffic in some cases. The value of commuter rail is of course disputed since its fast running times tend to encourage decentralization from the center city, but

» Mayor Rob Ford’s claim that he can build new subway with little public financing looks increasingly unlikely. But value capture remains one of many funding devices that should be considered seriously by transit agencies.

Last fall’s mayoral election in Toronto was a watershed moment for Canada’s largest city; in electing conservative Rob Ford to the top post, the public essentially rejected the approach that had been taken by former Mayor David Miller. For transportation, the change was particularly dramatic. Whereas Mr. Miller had advocated a network of surface-running light rail lines called Transit City, Mr. Ford lambasted this approach as a “war on cars” and declared that the only public transportation projects he would pursue would be in subways.